The present invention relates generally to a sheet accumulating system and, more particularly, to a sheet accumulating system that uses a continuous web cutter for providing cut sheets and a right-angle transport device for stacking the cut sheets.
Continuous web cutters are known in the art. A typical continuous web cutter is shown in FIG. 1. FIG. 1 shows a mass mailing insertion machine 1, which uses a continuous web cutter 10 to cut a continuous web of material 20 into cut sheets, and provide the cut sheets to a sheet accumulator 60 via a right-angle transport device 50. The cut sheets are accumulated into stacks in the sheet accumulator 60 and the stacks are inserted into envelopes in an envelope insertion station 70. As shown in FIG. 1, a continuous web of material 20 with sprocket holes on both side of the web 20 is fed from a fan-fold stack 18 into the web cutter 10, which has two moving belts with sprockets 12 (or tractors with pins) to move the web 20 toward a guillotine cutting module 16 for cutting the web 20 cross-wise into separate sheets. Perforations 30 (see FIG. 2a) are provided on each side of the web material 20 so that the sprocket hole sections of the web 20 can be removed from the sheets prior to moving the cut sheets to other components of the mailing insertion machine 1. In particular, the continuous web cutter 10, as shown in FIG. 1, is used to feed two webs 22, 24 of material linked by a center perforation 26. As shown, a splitter 14 is used to split the linked webs 22, 24 into two separate webs before the webs can be simultaneously cut by the cutting module 16 into two cut sheets 42, 44, as shown in FIG. 2a. This type of web cutter is also known as a 2-up cutter. As shown in FIG. 2a, the sheets 42, 44 are moved substantially along a direction 102 toward a right-angle transport device 50 so that both sheets are moved along the same line in a different direction 104 as they exit the right-angle transport device 50.
Right angle transport devices are known in the art. For example, Auerbach et al. (U.S. Pat. No. 5,664,772) discloses a right-angle transport device having two or more sheet turn-over modules, wherein the turn-over modules are placed at 45 degrees in the path of two or more sheets moving in a side-by-side fashion so that these sheets are turned over while their moving direction is changed by 90 degrees. Two turn-over modules 52, 54 are shown in FIG. 2a. Before encountering the turn-over modules 52, 54, the cut sheets 42 and 44 are moving side-by-side at the same speed, with their leading edges 142, 144 substantially in-step with each other. However, after emerging from the turn-over modules 52, 54, as shown in FIGS. 3d and 3e, the cut sheet 42 leads the cut sheet 44 by a distance D. This is because the two cut sheets 42, 44 travel on two different paths. As shown in FIG. 2b, the cut sheet 42 travels on a shorter inner path 112, while the cut sheet 44 travels on a longer outer path 114. The length of the outer path 114 (from Xxe2x80x2 to M) is greater than the length of the inner path 112 (from X to M) by a distance OM, which is substantially equal to D.
FIGS. 3a to 3e illustrate how the turn-over modules 52, 54 are used to change the direction of the cut sheets 42, 44 so that they are moving substantially in the same path 116, with one sheet leading another in an overlapping manner. As shown in FIG. 3a, sheets 42, 44 move at the same speed 106 toward the turn-over modules 52, 54 along the first direction 102. The length of the sheets 42, 44 is denoted by the letter L and the width is denoted by the letter W. As shown in FIG. 3b, part of the sheets 42, 44 are turned over by the turn-over modules 52, 54 and the turned over sections move along the second direction 104, which is substantially perpendicular to the first direction 102. FIG. 3c shows that the sheets 42 and 44 are further engaged with the turn-over modules 52, 54. Because they move at the same speed 106, the sheets 42, 44 are turned over by the same amount. As the sheets 42, 44 emerge from the turn-over modules 52, 54, they move substantially on the same line along the second direction 104 with the inner cut sheet 42 leading the outer cut sheet 44. The sheets are partially overlapped with each other by an amount S, as shown in FIG. 3d. The overlapped amount S is substantially equal to the difference between L and W. When the sheets 42, 44 are completely disengaged from the turn-over modules 52, 54, they are overlapped by the same amount S, as shown in FIG. 3e, if they are not moved by another moving mechanism in a different way.
The partially overlapped sheets 42, 44 form a 2-sheet packet. The overlapped amount in this 2-sheet packet is essential for collation in the sheet accumulator 60. If the difference between the length L and the width W of the sheets is very small, the small overlapped amount of the two cut sheets may cause a paper jam. If the width W is equal to or greater than L, then the sheets do not overlap with each other after they emerge from the turn-over modules 52, 54, which can cause problems in collation.
In order to achieve a desirable overlapped amount in a 2-sheet packet, Ifkovits et al. (U.S. Pat. No. 6,443,447) uses rollers of different speeds to separately drive the two cut sheets 42, 44 toward the turn-over modules 52, 54. More specifically, the driving speed for the inner cut sheet 42 is lower than the driving speed for the outer cut sheet 44. The use of different speeds would complicate the design of the mass mailing insertion machine because motors of different speeds are needed. Use of different speed motors in a higher velocity system is impractical because significant path length must be added to both paths in order to provide the design overlap.
Furthermore, in a mass mailing insertion machine, as shown in FIG. 1, the collation of sheets in the accumulator 60 requires that a minimum allowable gap is provided between two consecutive packets. The minimum allowable gap is determined by the time required for the trailing edge of the preceding packet to settle in the accumulator before the leading edge of the following packet arrives. The gap between consecutive packets is mainly determined by the cutter rate of the web cutter 10 and the moving speed of the cut sheets. In a machine, as disclosed in Ifkovits et al., if the speed for the inner path is 121 ips (inch per second) and the speed for the outer path is 144 ips, the inter-packet gaps at different cutter rates can be calculated as follows:
Depending on an accumulator""s design, it is generally desirable to have a minimum allowable gap of 2.94 inches or 20 ms between two consecutive packets. This gap is calculated by assuming that the sheets attain their velocity after they are cut by the cutting module 16 and driven by nips in the right-angle transport device 50. Without the speed differential, the resulting gap for a 25K cutter operated at 144 ips would be 1.38 in (10 ms). In practice, the gap is somewhat non-deterministic due to the soft nips used in the web cutter and in the right-angle transport device. At any rate, while the machine as disclosed in Ifkovits et al. increases the inter-packet gap and helps solve the problem regarding the overlapped amount between two sheets in a packet, it is difficult to achieve a minimum allowable gap beyond the cutter rate of 27K.
It is advantageous and desirable to provide a method and device for increasing the overlapped amount of the cut sheets as they exit the right-angle transport device and, at the same time, increasing the inter-packet gap as the packets arrive in an accumulator.
It is a primary objective of the present invention to increase the overlapped amount of cut sheets in a sheet packet as they exit a right-angle transport device. If so desired, the overlapped amount in the sheet packet can be increased so that they are totally overlapped with each other such that the leading edge of one sheet is substantially in-step with the leading edge of another. It is another objective of the present invention to achieve a desirable inter-packet gap in the accumulator of a mass mailing insertion machine while increasing the cutter rate. These objectives can be achieved by compensating the pathlength of one or more cut sheets between the cutter module of the web cutter and the turn-over modules of the right-angle transport device.
Thus, according to the first aspect of the present invention, there is provided a path deflection device to be used in a sheet accumulating system. The system comprises:
a continuous web cutter for cutting a continuous web of material into groups of cut sheets, each group of cut sheets comprising at least a first sheet and a second sheet moving substantially side-by-side along a first direction, wherein the first sheet moves in a first path and the second sheet moves in a second path substantially equal to the first path in length; and
a right angle transport device for changing the moving direction of the sheets from the first direction to a second direction substantially perpendicular to the first direction, such that the first and second sheets move in a same path in the second direction, with the second sheet traversing an additional path in the second direction, causing the first sheet to lead the second sheet in the second direction in an overlapping manner with an overlapped amount. The path deflection device comprises:
a channel having an entrance point and an exit point, disposed in the first path such that the entrance point is located at a first point of the first path and the exit point is located at a second point of the first path; and
a deflection mechanism disposed at the entrance point of the channel for causing the first sheet to deviate from the first path at the first point, to move through the channel and exit the channel at the exit point so that the first sheet continues to move in the first path from the second point toward the right angle transport device, wherein the channel has a channel length greater than the distance between the first point and the second point of the first path so as to compensate for the additional path traversed by the second sheet in the second direction, thereby increasing the overlapped amount.
Advantageously, the first and second sheets have a width and a length, the length substantially parallel to the first and second paths, wherein the difference between the channel length and the distance between the first point and the second point of the first path is substantially equal to or small than the width of the first and second sheets.
According to the second aspect of the present invention, there is provided a method of sheet accumulation. The method comprises the steps of:
cutting a web of material into groups of cut sheets, wherein each group of cut sheets comprises at least a first sheet and a second sheet moving substantially side-by-side along a first direction, wherein the first sheet moves in a first path and the second sheet moves in a second path substantially equal to the first path in length;
changing the moving direction of the sheets from the first direction to a second direction substantially perpendicular to the first direction, such that the first and second sheets move in a same path in the second direction, with the second sheet traversing an additional path in the second direction, causing the first sheet to lead the second sheet in the second direction in an overlapping manner with an overlapped amount; and
increasing the first path in order to compensate for the additional path traversed by the second sheet in the second direction, thereby increasing the overlapped amount.
Advantageously, the first pathlength is increased by a path deflection device having a curved path disposed in the first path for replacing a section of the first path, wherein the curved path has a deflection pathlength and the replaced section has a section length smaller than the deflection pathlength or substantially equal to the width of the first and second sheets.
Advantageously, the first and second sheets have a width and a length, the length substantially parallel to the first and second paths, wherein the difference between the deflection pathlength and the section length is smaller than or equal to the width of the first and second sheets.
According to the third aspect of the present invention, there is provided a sheet accumulating system. The system comprises:
a continuous web cutter for cutting a continuous web of material into groups of cut sheets, each group of cut sheets comprising at least a first sheet and a second sheet moving substantially side-by-side along a first direction, wherein the first sheet moves in a first path and the second sheet moves in a second path substantially equal to the first path in length;
a right angle transport device for changing the moving direction of the sheets from the first direction to a second direction substantially perpendicular to the first direction, such that the first and second sheets move in a same path in the second direction, with the second sheet traversing an additional path in the second direction, causing the first sheet to lead the second sheet in the second direction in an overlapping manner with an overlapped amount; and
a path deflection device, disposed in the first path, for compensating for the additional path traversed by the second sheet in the second direction, thereby increasing the overlapped amount.